新疆阿勒泰乌拉斯沟铅锌铜矿床的富CO_2流体及其地质意义

CO_2-rich Fluids and Their Geological Significance of the Wulasigou Pb-Zn-Cu Deposit,Altay,Xinjiang

乌拉斯沟铅锌铜矿床位于新疆阿尔泰南缘克兰火山–沉积盆地。本矿床分为铜、铅–锌两个矿化带,矿体赋存在下泥盆统康布铁堡组上亚组,容矿岩石为大理岩、绿泥石英片岩等。矿床内角砾状铅锌矿石反映了早期海相沉积成矿作用,矿床变形变质特征明显,其矿化石英脉可分为两个阶段:早阶段顺层石英脉和晚阶段切层硫化物石英脉。石英脉中流体包裹体分为富CO_2包裹体、碳质流体包裹体和部分水溶液包裹体,含子晶包裹体。显微测温结果显示,早阶段石英脉中富CO_2包裹体,CO_2相的三相点温度(Tm,CO_2)范围在–62.3~–58.5℃,CO_2笼合物熔化温度(Tm,clath)为0.5~7.5℃,部分均一温度(Th,CO_2)集中在5.0~21.0℃,均一温度(Th,total)集中在285~378℃,所计算的盐度变化于4.9%~15.1%Na Cleqv之间,密度为0.84~0.97 g/cm^3,最低捕获压力为260~360 MPa。晚阶段石英脉中,富CO_2包裹体的CO_2三相点的温度(Tm,CO_2)为–61.9~–56.9℃,T_(m,clath)为0.4~9.5℃,Th,CO_2为9.0~28.0℃,Th,total范围为242~389℃,盐度分布于1.0%~15.5%Na Cleqv之间,密度为0.55~0.98 g/cm^3,最低捕获压力范围为180~370 MPa。激光拉曼探针测试显示包裹体除含CO_2外,还含有不定量的CH4和N2。铜矿化石英脉的流体以富CO_2为特征,为中高温、低盐度、中低密度的H_2O-NaCl-CO_2±CH_4±N_2变质流体,与造山–变质成因有关。

The Wulasigou Cu-Pb-Zn deposit is one of the Cu-Pb-Zn polymetal deposits in the Devonian kelan volcanic- sedimentary basin of Southern Altaids. The origin of the deposits in the basin is still controversial yet. They were considered as volcano-sedimentary-related in many early literatures. Recently, metamorphic fluids were recognized by some authors. The Wulasigou Cu-Pb-Zn deposit occurs in the Lower Devonian Kangbutiebao Formation, which is composed of metamorphosed rhyolite, quartz schist, and metamorphic crystal tuff. There are two stages of vein-type Cu mineralization, the lentoid or streaked early quartz veins （QI） and the later sulfide-quartz veins （QII）. Microthermometric studies show that solid CO2 melting temperatures （Tm,co2） of Lmo-Lco2 inclusions in （QI） are mostly in the range of-62.3--58.5 ℃, clathrate melting temperatures （Tm,clath） are in the range of 0.5~7.5 ℃, partial homogenization temperatures （Th,co2） vary from 5.0-21.0℃, and the total homogenization temperatures （Th,total are in the range of 285-378℃, with the salinities and densities of 4.9%~15.1% NaCleqv and 0.84~0.97 g/cm3 respectively. The later quartz veins （QII） have -61.9- -56.9 ℃ of Tin,co2, 0.4-9.5 ℃ of Tm,clath, 9.0-28.0 ℃ of Th,CO2, and 242-388 ℃ of Th,total, with the salinities of 1.0%-15.5%NaCleqv and densities of 0.55~0.98 g/cm3. The lowest trapping pressures of fluid inclusions in QI are 180-370 Mpa and 260-360 MPa in QII. Laser Raman spectroscopy revealed that the CO2-rich fluid inclusion contains major contents of CO2 and a little variable component of CH4 and/or N2 in CO2 phases. The fluids of Cu-bearing veins from the Wulasigou deposit are characterized by CO2-rich, medium-high temperatures, low salinities, medium-low densities, and can be considered as H20-CO2-NaCl＋CHa＋N2 system. The ore-forming fluids should be related to orogenic and metamorphic hydrothermal fluids.